The subject matter disclosed herein relates generally to control of an electric motor and, more specifically, to a system for detecting vibrations using sensors mounted to the electric motor and reducing the detected vibrations using a controller connected to the electric motor.
Electrical rotating machines, such as electric motors or generators, have become widespread and are found in numerous applications and configurations. Electric machines include a stationary component (i.e., the stator) and a rotating component (i.e., the rotor). In electric motors, a magnetic field is established in the rotor, for example via magnets mounted to the rotor or via an electrical current applied to or induced in a coil wound on the rotor. A second, rotating magnetic field is established as a result of the application of a controlled voltage to the stator, and the rotation of the magnetic field in the stator causes the magnetic field in the rotor to rotate, thereby causing rotation of the rotor. A shaft or other drive member is mounted to the rotor and extends outside the rotor housing providing a mechanical coupling to a device, such as a gearbox, pump, or fan that is to be driven as the rotor rotates.
It is also known that motor controllers may be provided to convert input power, from either an alternating current (AC) source or a direct current (DC) source, to the controlled voltage applied to the stator. In certain applications, high performance of the motor and the controlled machine is desired. For example, a servo motor may position a machine tool with high speed and tight position tolerances for repeatable manufacturing of components. The servo motors may be mounted to a machine and coupled, via a gearbox to a drive member, such as ball-screw or rack and pinion used to position one axis of the machine.
Due to the rotational nature of an electric machine, imbalances, for example, on the rotor shaft; misalignments, for example, between the motor shaft and the gearbox; complaint mechanical loads, such as couplings between a motor shaft and a gearbox; or even torque ripple due to machine construction, can result in vibrations or resonance being generated within the control system. These vibrations or resonances may not occur throughout the operating range of the motor but may occur at specific operating frequencies. Such vibrations or resonances may result in increased wear on the motor or require the responsiveness, of the motor controller to be reduced to avoid the resonance, resulting in reduced throughput of the controlled machine. Thus, it would be desirable to detect such vibration to provide improved operation of the controlled machine.
Historically, sensors have been mounted to the motor to detect vibrations in the motor. A motor controller may receive a signal corresponding to the vibration and adjust an operating parameter in the motor controller in response to the vibration signal. However, multiple potential sources of vibration exist in a motor, and each source of vibration may require different adjustments to the control of the motor to reduce the level of vibration. With existing vibration detection sensing systems, it is difficult or impossible to determine the source of the vibration. Thus, it would be desirable to provide an improved system for monitoring vibration of an electric machine and for adjusting operation of the motor to reduce vibration detected in the motor.